Developments in antibody engineering and recombinant DNA technology have made it possible to generate forms of recombinant antibody fragments which, in many ways, are functional substitutes of larger intact immunoglobulin molecules. Single heavy domain antibody fragments (“dAb”) have been the subject of several reports in the patent and scientific literature. The literature reports efforts to generate phage display libraries of such fragments for biopanning against a target ligand.
U.S. Pat. No. 5,702,892 ('892) discloses a phage display library constructed in an M13 derived expression vector, in which recombinant phage of the library contain a polynucleotide encoding a fusion protein which comprises a phage coat protein and an immunoglobulin heavy chain binding-fragment. The heavy-chain binding-fragment spans from a position upstream of CDR1 to a position downstream of CDR3. '892 describes that the DNA sequence encoding the CDR3 region and/or the CDR1 region may be randomly varied so that the population of phage expresses a series of potential heavy chain binding domains for panning against the target ligand. U.S. Pat. No. 5,759,808 discloses a phage display library comprising a population of phage based on random variation of a cDNA sequence obtained from lymphocytes of camelids previously immunized with target antigens. Camelid heavy chain antibodies occur naturally, in a composition of about 45%, as heavy chain dimers. Heavy chain antibodies specific for a target antigen may be generated by immunizing a member of the camelid species with the target antigen (see Lauwereys et al. (1998) The EMBO J. 17, 3512-3520).
Hamers-Casterman et al. (1993) Nature 363, 446-448 report that camelid heavy chain antibodies are naturally more hydrophilic at amino acid residues at locations 44, 45 and 47 (Kabat numbering system), in FR2, which corresponds to the surface where they normally contact the VL domain Another salient feature of a camelid VH is that it generally has a comparatively longer CDR3 with a high incidence of cysteines and thus may form, via paired cysteines in CDR1 and CDR3, exposed loops, which are more amenable to binding into cavities such as the active site of enzymes and antibodies (Desmyter et al. (1996) Nat. Struct. Biol. Vol. 3, No. 9, p. 803). However, it has been questioned whether single domain antibodies with desired affinities can be generated with such configurations in the absence of prior immunization, i.e. with a naïve library (Lauwereys et al. (1998) supra).
The present invention discloses advances in the technology related to creating libraries containing immunoglobulin-like proteins that specifically bind target ligands eg. antigens.